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Is this normal for a 30 gal lowboy?

02-10-2009, 08:19 PM

I received a call from one of my customers yesterday, saying that his wife ran out of hot water after being in the shower for only 5 minutes. When I went there today the first thing I did was run the hot water over my thermometer to see how long the hot water would last. It was running out of a newer style Kohler lavatory faucet so I believe at full flow it was running about 2.2 gpm. (Obviously a newer shower head flows only about half of that). I had 130 degree water for a full 5 minutes then it started to drop in temperture slowly...about 3 degrees per minute. Is it normal for a 30 gallon lowboy with two 3500 watt elements(208 volts) to supply only 11 gallons of consistent 130 degree water for the first 5 minutes? I checked both elements and both thermostats....they all work fine. Doea anyone know if there's a chart from one of the manufacturers that will tell me recovery rates for different size water heaters with different elements in them? Thanks.

Comment

Mike, I appreciate the help but I think you were off on one thing. The stat is set to 130 but that is not the temperture rise. The temperture rise is 130 minus the inlet temp(about 80 degrees down here in FL). So the temp rise is 50 degrees. Thnaks for the formula though...I appreciate it.
-James

Comment

If i am not mistaken an electric heater will put out about what thier capacity is, thus the 30 gallon heater should put out roughly 30 gallons, I would say plus or minus 10. This is called thier first hour rating. I am curious about how you tested the thermostats. I would peg this for either a bad lower element and/or stat or a bad dip tube. With an electric heater only one element is on at a time. The upper thermostat has to satisfy before the lower is energized. During a long draw of hot water the lower element will become energized to heat the incoming water. In order to test the lower stat you would have to wait until the upper stat satisfies and then determine if signal is getting to the lower stat and then to element.

Comment

I was considering the dip tube, but from my previous experiences if the dip tube is bad then you usually lose hot water quicker then I was. I checked both stats with an amp meter....first the upper which drew about 13 amps, then i lowered the temp on it and the lower stat kicked on...drawing close to the same 13 amps. I installed the heater about 6 months ago and it was on a Sunday when I had no A.O. Smiths on my truck so I had to get a GE from Home Depot. I put in some new 4500 Watt elements(about 4000 watt for 208 volts) and it now draws about 15 amps for each element. The faucet had the original aerator on it but I know that since this is the second floor of a 13 story condo, they get almost 90 psi water pressure.(Now that I think about it, I don't think they had a pressure reducing valve on the main). What is the standard faucets 2.2 GPM based on....60 psi?

Comment

No, T& P is fine....everything seems to be fine, that's what's bugging me. I just called them and they said that they have plenty of hot water now.....hmmmmmmmmm now I'm really curious. All I did was change the elements to slightly higher wattage. Maybe the originals in the GE's are garbage, wouldn't that be a shocker! HAHA

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